The present invention relates to an improved out-of-circuit ball preventing structure for ball screw nuts of the ball circulation tube type and of the ball circulation piece type.
A ball screw apparatus has a ball circulation passage for circulating balls therein. Structures of the ball circulation passage are known in that a ball circulation tube or a ball circulation piece is provided in the barrel portion of the ball screw nut and that ball circulation curved passages are arranged on both front and rear ends of the ball screw nut. Each nut has one or more circulation passages (hereinafter, refer as circuits) using the ball circulation tube or ball circulation piece. In the case where the nut has a plurality of circuits, a groove portion through which no balls circulate, i.e., through which no balls pass (hereinafter, refer as an out-of-circuit groove) is present between one circuit and other circuit(s) adjacent thereto.
For example, FIGS. 5 to 7 show a ball screw nut of ball circulation tube type, in which an out-of-circuit groove Sout is present between a first circuit S1 and a second circuit S2.
To assemble such a ball screw nut 2 of the ball circulation tube type, a screw shaft 1 is inserted into the ball screw nut 2 without circulation tubes 3; balls B are sequentially introduced from ball circulation holes 4 in the barrel portion of the nut to load the balls B into ball passages formed by screw grooves 2a over the inner circumferential surface of the ball screw nut 2 and screw grooves 1a confronting the screw grooves 2a over the outer circumferential surface of the screw shaft 1. Once the balls B have been loaded up to the ball circulation holes 4, both leg portions of each U-shaped circulation tube 3 with balls B loaded separately in advance are inserted into the ball circulation holes 4, and the ball circulation holes 4 are then fixed to the barrel portion of the nut with fasteners to complete the assembling.
In the case where there are two ball circulation circuits, no balls are normally present in the out-of-circuit groove Sout between the screw groove S1in of the first circuit S1 (in-circuit groove) and the screw groove S2in of the second circuit S2. However, if some balls are erroneously introduced into the out-of-circuit groove during the ball loading operation, tongue portions 3a at both ends of the circulation tube 3 are damaged, thereby making it likely that the function of the ball screw will be impaired.
A deflector 5 such as shown in FIG. 8 has heretofore been employed as a structure for preventing erroneous insertion of a ball into such out-of-circuit groove Sout (out-of-circuit ball Bout). The deflector 5 is attached to the out-of-circuit groove Sout of the ball screw nut 2 as shown in FIGS. 9 and 10.
However, the conventional out-of-circuit ball preventing structure for a ball screw nut is not only cumbersome in terms of having to specially make and attach the complicatedly shaped iron deflector 5 but also costly in terms of material, the number of machining and assembling steps, as well as the number of parts.